The free-living nematode Caenorhabditis elegans is a popular model for the study of many biological phenomena, including development. I have isolated and characterized nine rad (for abnormal radiation sensitivity) mutants of C. elegans. More mutants, which are sensitive to DNA-damaging agents and therefore putatively defective in DNA repair, will be isolated. These will be analyzed genetically to provide additional information as to the factors which govern DNA repair capacity. The biochemistry of DNA repair in repair-proficient and repair-deficient strains will also be examined. First, using alkaline sucrose gradient centrifugation, the ability to excise DNA damage will be determined. Second, the amount of unscheduled DNA synthesis after DNA damage will be assayed. Both experiments provide information about excision repair, one major form of DNA repair. A second DNA repair system, post-replication repair, will be measured by testing animals for their ability to synthesize high molecular weight DNA on a radiation-damaged DNA template. As preliminary evidence indicates that DNA repair is developmentally regulated in C. elegans, tests will be performed on animals at more than one developmental stage. A number of additional experiments will focus on the developmental regulation of DNA repair in specific cell lineages. The effects of DNA-damaging agents on cell division will be examined, with the hope of correlating the developmental fates of particular cells with their sensitivities. In addition, biochemical testing, in which fluorescence over specific nuclei will be quantitated, will allow DNA repair capacity to be monitored in specific cells.